1. Field of the Invention
The invention relates to methods, each of which comprises improvements forming a part of a system for the complete treatment of sanitary sewage. More particularly, one method encompasses treatment in a waste stabilization pond in which the BOD level of such sewage is reduced by aerobic decomposition through action of algae, followed by removal of the algae in an algae removal pond. The invention also contemplates in a later stage of treatment use of a polishing pond having a weir for aeration and exposure of treated effluent to sunlight. The invention also encompasses for an early stage of treatment use of a facultative pond in which combined aerobic and anaerobic decomposition takes place, permitting a substantially increased volume of sewage to be treated while avoiding drawbacks commonly associated with entirely anaerobic treatment.
2. Description of the Prior Art
It is known to grow microorganisms for oxidation of waste matter to reduce its BOD by 85% to 95%, such as in the method and apparatus described by Torpey in U.S. Pat. No. 3,849,303, issued Nov. 19, 1974. A drawback of the method and apparatus of Torpey is the requirement for rotating biological contactors, which limits the size and volume of the container for carrying out the process, as well as the volume of sewage that can be treated.
U.S. Pat. No. 3,260,368, issued July 12, 1966, to Wagner et al, discloses a sewage disposal system employing apparatus which has an upper chamber where aerobic digestion takes place, as well as a lower chamber for anaerobic digestion. Disadvantages associated with the Wagner system include high cost of construction, involving provision of equipment for heating, aspirating, and circulating the liquid undergoing treatment. Aeration by introduction of compressed air necessitates equipment, such as compressors, aerators, and associated piping. Moreover, separate aerobic and anaerobic tanks are required in the Wagner method. Separate tanks for aerobic and anaerobic treatment are also disclosed in U.S. Pat. No. 3,666,106, issued May 30, 1972, to Green. U.S. Pat. No. 3,878,101, issued Apr. 15, 1975, to Kennedy, shows weir drains for removing treated sewage. Such drains, however, do not provide substantial exposure to air and sunlight, and require special fabrication of channels. Seidel in U.S. Pat. No. 3,770,623, issued Nov. 6, 1973, teaches removal of suspended and dissolved pollutants through use of vegetation rooted in beds into which the liquid is introduced.
Other patents disclosing prior art treatment methods and apparatus are the following:
U.S. Pat. No. 942,697--Dec. 7, 1909--Allen PA0 U.S. Pat. No. 2,657,178--Oct. 27, 1953--Robinson PA0 U.S. Pat. No. 3,036,713--May 29, 1962--Lambeth PA0 U.S. Pat. No. 3,047,492--July 31, 1962--Gambrel PA0 U.S. Pat. No. 3,166,501--Jan. 19, 1965--Spohr PA0 U.S. Pat. No. 3,337,454--Aug. 22, 1967--Gruenwald PA0 U.S. Pat. No. 3,443,694--May 13, 1969--Malinovsky PA0 U.S. Pat. No. 3,561,945--Feb. 9, 1971--Kilburn PA0 U.S. Pat. No. 3,563,383--Feb. 16, 1971--Hellquist, et al. PA0 U.S. Pat. No. 3,591,492--July 6, 1971--Neuspiel PA0 U.S. Pat. No. 3,638,793--Feb. 1, 1972--Peck PA0 U.S. Pat. No. 3,682,307--Aug. 8, 1972--Cook, et al. PA0 U.S. Pat. No. 3,756,946--Sep. 4, 1973--Levin, et al. PA0 U.S. Pat. No. 3,835,038--Sep. 10, 1974--Heaney PA0 U.S. Pat. No. 3,900,394--Aug. 19, 1975--Rongved PA0 U.S. Pat. No. 3,914,173--Oct. 21, 1975--Call, et al. PA0 U.S. Pat. No. 3,933,640--Jan. 20, 1976--Kirk PA0 U.S. Pat. No. 3,959,124--May 25, 1976--Tchobanoglous.